Granulation apparatus

ABSTRACT

Apparatus for the granulation of a predetermined substance provided in fluid, semi-fluid and similar state, comprising a prilling tower.

FIELD OF APPLICATION

In its most general aspect the present invention refers to an apparatusfor the granulation of a chosen substance provided in fluid, semi-fluidand similar state, like for example a melted substance.

In particular, the present invention refers to an apparatus comprising atower (also called prilling tower in the rest of the description) insidewhich and at the top of which a device is supported that divides saidsubstance into drops and simultaneously distributes them in said tower.Then the barely formed drops of the predetermined substance fall throughthe tower, in counter current to a flow of rising gas which solidifiesthem in substantially spherical granules (so-called “prills”).

PRIOR ART

It is known that granulation techniques of substances generally providethat the predetermined substance is made available in a “fluid”condition, for example dispersed or dissolved in a liquid phase, or elseeven in melted state; then that it is divided into drops, and then thatsuch drops are cooled so as to “transform” them into solid granuleswhich are “monodispersed” as much as possible, in other words of a sizeand shape that are as uniform as possible.

And it is known that one of the most widespread granulation techniquesuses a generally cylindrical tower, inside and at the top of which issupported a rotating bucket (also known as prilling bucket in the restof the description and in the subsequent claims) fed with the fluidsubstance to be granulated, which provides for the formation of dropsand their distribution inside the tower. At the base of said tower isprovided a gaseous fluid blowing system which, rising in counter currentto said drops, transforms them into granules.

It is equally known that to obtain, through an apparatus of theaforementioned type, granules of the chosen substance with optimalyield, the drops of said substance have to be uniformly distributed onthe entire section of said tower. Moreover, it is required that saiddrops have a homogeneous, if not actually totally identical, shape andsize, in order to obtain granules of said substance all of the samegiven size (i.e. monodispersed granules).

Now, it is also known that the drops uniformity of distribution insidethe prilling tower is—among others—proportional to the rotation speed ofthe bucket that produces and distributes them. Consequently, it is knownthat, to optimise the distribution of the barely formed drops inside theprilling tower, it is required that the aforementioned bucket rotates ata speed, which is more and more higher with the increase of the towerdiameter. For example, for tower of big diameter (and thus of highcapacity), such rotating speed is in the order of 250 rpm.

To do so, in accordance with the prior art, the prilling bucket,positioned inside and at the top of the tower, is mounted at the end ofa motorized shaft, with which it is made integral in rotation, saidshaft extending for an appropriate portion outside of the prillingtower, where an engine of appropriate power is kinematically connected.

To create drops of homogeneous size and shape, in other words to obtaingranules which are monodispersed as much as possible, the prior artteaches to give the prilling bucket a vibration which is as regular aspossible and preferably extending in the vertical direction.

To do so, still in accordance with the prior art, an electronic orpneumatic vibrator device is used, associated with said motorized shaft,in particular with the portion thereof outside of the tower and, throughsaid shaft, the vibration is transmitted to the prilling bucket integralwith it.

An example of granulation apparatus of the aforementioned type isdescribed in patent U.S. Pat. No. 4,585,167.

Now, if on the one hand an appropriate vibration of the prilling bucketsatisfies the requirement of forming drops homogeneous in size andshape, on the other hand the transmission of said vibration to theprilling bucket, through the same motorized shaft which provides to itsrotation, has forced the adoption of much reduced rotation speeds of thebucket with respect to those required for optimal uniformity ofdistribution and this to avoid clear dangers of structural breakage andthe like.

An apparatus of the aforementioned type, as taught by the prior art tosolve the outlined problem, is clearly a compromise solution and, assuch, does not satisfy particularly the requirement of uniformdistribution of the drops of substance to be granulated.

In other words, such an apparatus does not allow the production ofmonodispersed granules in an efficient manner, such as to be able tosatisfy the ever growing productivity requirements requested byindustry.

SUMMARY OF THE INVENTION

The technical problem underlying the present invention is that ofproviding an apparatus for granulating a chosen substance, havingstructural and functional characteristics such as to allow an optimaldistribution of the drops of substance inside and at the top of aprilling tower, together with obtaining granules of said substancesubstantially completely monodispersed, overcoming the cited drawbackswith reference to the prior art described above.

This problem is solved according to the invention by an apparatus forthe granulation of a substance provided in fluid, semi-fluid and similarstate comprising a prilling tower, a prilling bucket revolvinglysupported inside and at the top of said tower, a driving shaft,revolvingly supported at the top of said tower and extending in theaxial direction thereof, said shaft having at least one end portionassociated with said prilling bucket to command it into rotation, and adevice to apply vibration to said bucket, characterized in that thebucket is mounted in a sliding way on said driving shaft in said axialdirection and it is integral with it in rotation and in that said deviceis directly associated with said bucket to make it vibrate in said axialdirection.

Advantageously, said device is mounted on said bucket, inside theprilling tower.

The sliding coupling, for example with grooved or feather profiles,between driving shaft and prilling bucket and the assembly of thevibration device directly on the bucket itself, ensure that the drivingshaft is not “mechanically” influenced by the vibration of the bucket(i.e. it is not made to vibrate). In other words, the vibrationintensity given to the prilling bucket and the speed of rotation thereofhave absolutely no influence upon each other.

Therefore, it is possible to adopt, case by case, both the optimal speedof rotation for an optimal uniformity of distribution of the dropsformed by the bucket, and the optimal intensity of vibration for thedesired homogeneity of size and shape of said drops.

In short, the apparatus of the present invention allows to obtainmonodispersed granules of the chosen substance, with a substantiallyimproved yield with respect to what has been possible up to now withanalogous apparatuses of the prior art.

Further features and the advantages of the apparatus according to thepresent invention will become clearer from the following description ofan indicative and non-limiting example of an embodiment thereof, madewith reference to the attached drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic view of an apparatus according to the presentinvention;

FIG. 2 shows a schematic and enlarged view of a detail of the apparatusof FIG. 1.

FIGS. 3 and 4 represent further enlarged views of the same detail ofFIG. 2, seen from two directions perpendicular to each other.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

With reference to FIG. 1, an apparatus according to the presentinvention comprises a prilling tower 1, the cylindrical shell 2 ofwhich, with vertical axis A-A, is closed at the opposite ends by a baseplate 3 and a top wall 4 (top or top panel) of the tower 1.

In a totally schematic way, with 5 and 6 are indicated ducts for theinput of a continuous rising flow of a predetermined gas (for exampleair) into the tower 1, and near to the base 3 thereof, with appropriateand predetermined flow rates and temperatures for the granulationprocess which one intends to actuate in said tower. Analogous ducts areindicated with 7 and 8, provided at the top 4 of said tower 1, for thedischarge of such a flow of gas and of what may be “subtracted” by it tothe fluid substance to be granulated.

The top wall 4 is crossed centrally by a tubular cylindrical hopper orduct 9, for the input of said fluid substance in the granulation tower1. This duct 9 extends coaxially to the shell 2, is supported fixed,with conventional and not shown means, by the top wall 4 thereof, andhas a portion 9 a outside of said shell and a portion 9 b inside it. Theportion 9 a of said duct 9 leads to a duct 10, for feeding the substanceto be granulated.

It should be noted that the cylindrical duct 9 is closed at the oppositeends, outside and inside said shell 2, by respective disc-plates 11, 12.Moreover, the inner portion 9 b is equipped with a plurality of slits13, extending along the generating lines thereof, circumferentiallydistributed on its side surface and of a size suitable for deliveringthe fluid substance to be granulated inside a bucket 15 (described indetail later on).

The tubular duct 9 is crossed axially by a motorized shaft 14, revolvingaround its vertical axis and passing trough openings 11 a, 12 a,centrally provided in the plates 11 and 12 respectively, of said duct 9,with possible interposition of gaskets (not represented).

Said shaft 14 has, on one side, a portion 14 a extending above thetubular duct 9, kinematically subjugated to and commanded into rotationby an engine 31, with appropriate characteristics. On the other side,the shaft 14 has a portion 14 b, with a reduced diameter, extendingbelow the duct 9, and with which it defines an annular shoulder 16.

Inside said shell 2 and near to the top wall 4 thereof, thesubstantially frusto-conical prilling bucket 15, having perforated sidewall 15 a, between upper and lower bases 15 b and 15 c, is coaxiallypositioned, to allow the supply of the fluid substance to be granulatedsplitted in a corresponding plurality of equal jets inside the tower 1.

At the lower base 15 c, outside the bucket 15, a base block or hub 17,of predetermined thickness is coaxially fixed.

Said base block 17 is axially crossed by a hole 18. In accordance with acharacteristic of the present invention, the portion 14 b of reduceddiameter of said motorized shaft 14 is engaged in a revolving andsliding manner in said hole 18. This coupling between motorized shaft 14and prilling bucket 15, is substantially of the type with grooved orfeather profile.

In particular and according to a preferred embodiment, such a couplingis obtained (FIGS. 3, 4) through frontal engagement between the free end14 c of the portion 14 b of said motorized shaft 14, and a disc 19 fixedto said portion 14 in predetermined distanced relationship from it.

More specifically, in said free end 14 c a first groove 21 is formed.Analogously, the base block 17 is provided at its lower free end, andextending from said hole 18 towards the external diameter thereof for apredetermined distance, with a second grove 22. Whereas, the disc 19 isequipped, on a face thereof, with a corresponding projection 23 intendedto engage, substantially as a keywasher, the aforementioned, aligned,grooves 21 and 22. The axial sliding of the bucket 15 on said shaft 14is ensured in this case by the fact that the height of said projection23 is less than the depth of the corresponding groove 21.

As quoted above, the disc 19 is fixed to the shaft 14, through a screw25 coaxial to the shaft 14, in predetermined distanced relationship fromthe base block 17 and between said base block 17 and the disc 19 a ring26 made from elastically deformable material is positioned, insubstantial contact with both.

An analogous ring 20, made from elastically deformable material ispositioned between the annular shoulder 16 and said lower base 15 c ofthe bucket 15.

The deformable material of rings 20, 26 can be an elastomeric material(such as rubber). In the alternative to rings 20, 26, springs (notshown), such as helicoidal springs or disc springs (Belleville springs),can be used.

As shall be seen more clearly from the rest of the description, saidrings 20 and 26 are functional at the vibration which one intends togive to the prilling bucket 15.

In accordance with a characteristic of the present invention, avibration of predetermined optimal intensity and mainly orientated inthe direction of the axis A-A of the tower 1 is given to said prillingbucket 15. For such a purpose an appropriate device is used, schematisedin 27, which, still in accordance with the present invention, is mounteddirectly on the bucket 15 and inside the same prilling tower 1.

According to a preferred embodiment, the device 27 is positioned in acarter 28, fixed to the base block 17 of said bucket 15. Advantageously,such device 27 is of the pneumatically actuated type. In this particularcase, the flow of air necessary for the operation of the device 27 isfed to it through a duct 29 in communication with a second duct 30,formed in the base block 17 and open in said carter 28. The duct 29extends above the prilling bucket 15, preferably up to the upper portion14 a of the driving shaft 14, from where it is placed in communicationwith an appropriate pressurised fluid source, not represented since itis per se known.

Preferably, the flow of air coming from the pressurized fluid source isfed through a duct 40 in an air connecting box 41, which is in fluidcommunication with the duct 29 and is supported fixed with conventionalmeans, such as feet 44, on the disc plate 11 of the cylindrical duct 9

According to the embodiment shown in FIG. 2, the duct 29 is axiallyformed in the driving shaft 14 and the air connecting box 41 isassociated thereto through suitable gas sealing means, such as gaskets42. In this case, the shaft 14 is also provided with at least oneconnecting duct 43 (two in the example) for putting into fluidcommunication said air connecting box 41 with the internal duct 29.

In the granulation device of the present invention, the driving shaft 14can carry out the important dual function of support and rotation of theprilling bucket 15, totally independently from the intensity ofvibration given to said bucket precisely because the coupling betweenbucket and shaft is of the sliding type (substantially using grooved orfeather profiles), whereas the device 27 is mounted directly on thebucket itself. The aforementioned apparatus therefore allows theprilling bucket to be rotated at high speeds, so as to ensure theoptimal distribution of the substance to be granulated, as well as togive said bucket high frequencies of vibration, so as to ensure theobtainment of definitely monodispersed granules. The whole thingavoiding those structural yielding dangers that the aforementionedcombination of speed of rotation and intensity of vibration determinesin granulation apparatuses of the prior art.

1. Apparatus for the granulation of a substance provided in fluid,semi-fluid and similar state comprising a prilling tower (1), a prillingbucket (15) revolvingly supported inside and at the top of said tower(1), a driving shaft (14), revolvingly supported at the top of saidtower (1) and extending in the axial direction (A-A) thereof, said shafthaving at least one end portion (14 b) associated with said prillingbucket (15) to command it into rotation, and a device (27) to applyvibration to said bucket (15), characterized in that the bucket (15) ismounted in a sliding way on said driving shaft (14) in said axialdirection (A-A) and it is integral with it in rotation and in that saiddevice (27) is directly associated with said bucket (15) to make itvibrate in said axial direction (A-A).
 2. Apparatus according to claim1, characterized in that said driving shaft (14) extends coaxiallythrough said prilling bucket (15) and has an end portion (14 b) coupledwith said bucket (15), in a sliding manner in the aforementioned axialdirection (A-A) and integral in rotation.
 3. Apparatus according toclaim 2, characterized in that said bucket (15) is coaxially equipped atthe bottom with a base block (17), crossed by an axial hole (18),engaged in a sliding way by said end portion (14 b) of said shaft (14).4. Apparatus according to claim 1, characterized in that said bucket(15) is mounted on said driving shaft (14) with a coupling substantiallyusing grooved profiles.
 5. Apparatus according to claim 3, characterizedin that said end portion (14 b) of said driving shaft (14) has a reduceddiameter with respect to that of said shaft (14) with which it definesan annular shoulder (16) and in that it comprises a disc (19) fixed tosaid portion (14 b) in a predetermined distanced relationship from it,between said annular shoulder (16) and the base block (17) and betweensaid disc (19) and the free end of said portion (14 b) of the drivingshaft (14) being positioned respective rings (20, 26) of elasticallydeformable material or springs.
 6. Apparatus according to claim 1,characterized in that said device (27) is mounted on said bucket (15),inside the prilling tower (1).
 7. Apparatus according to claim 6,characterized in that said device (27) is positioned inside a carter(28), fixed to said base block (17) below said bucket (15).
 8. Apparatusaccording to claim 7, wherein said device (27) is of the pneumaticallyactuated type.
 9. Apparatus according to claim 8, wherein a duct (29)for supplying compressed air to said device (27) extends from above saidbucket (15) to said base block (17) and is open in said carter (28). 10.Apparatus according to claim 9, wherein said duct (29) for supplyingcompressed air is partially axially extended in said driving shaft (14)and partially in said base block (17).
 11. Apparatus according to claim9, wherein said duct (29) for supplying compressed air is in fluidcommunication with a pressurised fluid source through an air connectingbox (41).